The patch above removes all the dependencies we don't need from the opencv MSYS2 package build, saving around 80MB of disk space.
The savings for our installer package are much smaller (~5MB) because we already trimmed it quite a bit and the file is compressed.

This should make things less brittle too: the opencv package seems to break very regularly in MSYS2 due to the huge amount of dependencies it has and because of the way the module loads them all - they would need to rebuild the package every time a dependency is updated.

Only problem is that the 32-bit version crashes hard, even the simple opencv_version.exe tool does... so r18290 disables webcam support in 32-bit builds.